Many of my clients are confused about whether they ‘need’ to take carbohydrate before training and events.
So, what’s the deal? Is carbohydrate beneficial, neutral, or detrimental when taken before training?
TL;DR – I think that on balance, for many people, carbohydrate is simply not necessary immediately before training and events. People typically don’t need to ‘boost’ their glycogen stores before training and, in my clinical experience, many suffer adverse effects like energy ‘crashes’ during activity if they have large or even moderate amounts of carbohydrate immediately before training.
- Carbs before training inhibits fat usage
- Carbs before training don’t offer a benefit to training and events < 90 min
- Higher carb intake overall, and the benefits of carbs before training appear in exercise bouts > 90 min
- Low-carb meals previous to training often result in longer times to exhaustion (better endurance)
- Lower-carb, ‘carb-appropriate’ strategies are likely to result in better preservation of glycogen and improved cardiometabolic health and improved fuel usage
Carbs Before Exercise – The Evidence
Carbohydrate ingestion before exertion is generally associated with improvements in performance for bouts of relatively intensive activity > 90 min but it reduces lipolysis (the breakdown of fat for fuel) and can lead to hypoglycaemia which can negatively affect performance in some individuals. (1-3) It’s also generally unnecessary for bouts of exercise under 90 minutes.
It has been demonstrated the a low-glycaemic index (GI) meal, more akin to one based on a normal, whole-food meal, as compared to highly refined processed carbohydrate foods (which typically have more rapid digestion and assimilation rates) result in lower respiratory exchange ratios (i.e. more fat used for fuel compared to ‘burning’ sugar) and greater fat utilisation. Lower-GI pre-exertion meals result in a 59% longer time to exhaustion, faster performance times, and reduced rates of perceived exertion. (4-6) It has similarly been demonstrated that a lower-carbohydrate meal of 30% CHO, 55% fat, and 15% protein is superior for enhancing endurance performance (time to exhaustion) than a high-carbohydrate meal of 71% CHO, 20% fat, and 9% protein. (7)
At low exercise intensities (< 70% of VO2max) for relatively short periods (20-50 min), there is no significant effect on performance from lower- vs higher-carb feedings but there is improved fat utilisation and reduced carbohydrate oxidation resulting from a low-carb meal, (8, 9) which provides a likely benefit for the preservation of glycogen which is a finite fuel resource when compared to the relative abundance of fuel in fat tissue. This has been further demonstrated in work by Achten and Jeukendrup. Both maximal fat oxidation and the intensity at which maximal fat utilisation was achieved, were reduced by the provision of 75 g of glucose in a graded exercise test. (10) A systematic review of these effects concluded that a lower glucose load is superior to a higher glucose load pre-exercise.
Overall, for most athletes, especially recreational ones, gym goers, and bodybuilders, there is no benefit to performance from specific high-carb pre-training or pre-event meals. There could even be reductions in fat-adaptation and fuel efficiency which could hinder longer term fat loss and impair metabolic health. A better option is to simply stick to a ‘carb-appropriate’ diet that provides sufficient fuel overall (including carbohydrate intake appropriate to your goals and your own ‘carbohydrate tolerance’), sufficient protein, and that is nutrient-dense. Pre-workout meals featuring protein can provide some benefit to lean body mass and recovery and post-workout protein and possibly carbohydrate supplementation (depending on nutrition strategy, goals, and metabolic tolerance to carbohydrate) can also be of benefit.
For events and training bouts longer than 90 minutes, there might be some benefit from pre-training meals containing higher levels of carbohydrate, especially if your overall carbohydrate intake is not sufficient to meet your carbohydrate requirements for higher-intensity (glycolytic or ‘sugar-burning’) activities. Remember that lower-carbohydrate athletes can store similar amounts of glycogen and restore it at the same rate as higher-carb consuming athletes, (11) BUT that all athletes can suffer glycogen depletion and negative effects of performance resulting from this if they are exercising for longer than 90 minutes at a time or have a high frequency of long-duration, high-intensity bouts of exercise. So, whether you prefer a low- or high-carb approach, carb-intake relative to your preferred diet type will still need to be higher if you are at risk of glycogen depletion.
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2. Kuipers H, Fransen EJ, Keizer HA. Pre-Exercise Ingestion of Carbohydrate and Transient Hypoglycemia During Exercise. Int J Sports Med. 1999;20(04):227-31.
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11. Volek JS, Freidenreich DJ, Saenz C, Kunces LJ, Creighton BC, Bartley JM, et al. Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism. 2016;65(3):100-10.